The invention relates to protecting the contents of a refrigerator truck trailer from lack of refrigeration caused by a failure in either of two power sources. More particularly, the invention is directed toward a back-up system that allows for the automatic switching from a first power source to a second power source upon the failure of the first. Even more specifically, the invention is primarily intended for use in refrigerator trucks having a diesel engine for operating a compressor and a standby motor operable by standard household A/C voltage wherein a standard cab control switch system is provided for operation of the refrigeration unit. In this last-mentioned type of system, the present invention is provided to offer a back-up automatic source switching system to said refrigeration control switch for automatically switching from the A/C line voltage to start the diesel generator or alternatively switching to the live A/C voltage line at the event of a failure of the diesel engine to continue an electrical operation of the compressor.
The prior art includes refrigeration units for trucks and fault or failure protection circuitry systems. Some of these utilize a hydraulic pump motor connection between the truck engine and the refrigerant compressing unit for eliminating previous disadvantages where separate internal combustion engines were used for driving compressors. Thus while dual modes of operation have been disclosed, the prior art has not suggested automatic means for shifting from the live service A/C line to the diesel engine for operating the compressor. Other systems utilize an over-running clutch for automatically disconnecting a power transmission from the electric motor. These type systems however are not found to have automatic means for starting a diesel engine when there is a power failure at the outlet box but merely provide for automatic disconnection of the power transmission from the electric motor.
Generally related power failure detection and switching systems have also provided for a very small trip window switching time that is accomplished by a synchronization of the zero-crossing of the primary power signal and the auxiliary power signal so that out-of-phase switchover problems, such as transformer saturation, do not occur. These systems have special use in computer operations. Similar systems provide back-up capabilities of the SPS-type consisting preferably of a static invertor operated only when a main current line fails. These systems are critical so that even intolerable 100 microsecond interruptions are avoided.
Of course other types of systems detect fault and isolate faults that occur in circuit boards, which provide for interrupting one circuit board from the main power supply when a short occurs.
Certain other refrigeration systems achieve a switchover from one power source to another when a power circuit voltage is within a predetermined range. Normally these systems utilize a high pressure switch connected to a relay means arranged with a voltage dependent means for deenergizing the relay means when pressure within a refrigeration system is not within a predetermined range. These also have required the use of time delay mechanisms connected to the relay means to allow the relay to be energized for a predetermined period of time during which the voltage dependent means may be by-passed. Such systems may select the appropriate mode of operation but usually require a delay for a predetermined time period during start up of an internal motor unit for the compressor when the voltage is not within a proper range. The primary goal of these types of system is the protection of the internal components of the refrigeration unit due to malfunction and involve technology known for at least about twenty years. Time delay startups are provided until voltage reaches a predetermined range. None of these systems provide back-up for failure of A/C power supply and/or standby motor failure with the capability to switch to and start the diesel generator motor on the refrigeration truck trailer; or an automatic switch back when A/C power is restored or upon reactivation of a previously failed standby motor.
The present invention is useful as a back-up for present cab commands/control circuit and switching systems which may be patched into the system of existing controls to provide necessary back-up and failure protection in a very efficient and economical modification.